Digital video is being used in an increasing array of applications ranging from personal computers (PC) and video conferencing to digital televisions (TV), set-top boxes, and personal video recorders (PVR). These varied video systems can process content from cable, satellite, and terrestrial broadcasts as well as streaming video and video-on-demand over the internet. The digital television industry faces several challenges in order to accelerate worldwide deployment of these technologies. It needs to make TV compelling and engaging, lower the cost of the roll-out of interactive services on digital TV, and develop a whole range of products in cost effective ways to take advantage of new market opportunities.
In particular, the fast-growing PVR systems (also known as Digital Video Recorders DVR) allow consumers to interactively choose which content they want to watch, from broadcast media or video-on-demand, and when to watch it. The viewers have the control, management rights, and personalization options on digital content. For example, the PVR/DVR systems allow viewers to record TV broadcasts from cable, satellite, or over-the-air to a hard disk. These systems record automatically, allowing viewers to pause, rewind, and replay live television. Furthermore, the PVR/DVR systems allow easy management of pre-recorded programs, and the ability to schedule and specify the recordings.
An important component of a PVR/DVR system is the storage medium. Traditionally, hard disks have been used as the storage medium. Newer systems have also employed conventional VHS tapes to record digital content in a compressed format, for example, the Digital VHS (D-VHS) format. These systems interface with digital video processing integrated circuits (ICs) using the IEEE 1394 digital interface. The format of digital content stored can range from full transport streams to partial transport streams and program streams.
Full transport streams contain fixed-size packets from several different compressed programs interleaved together. For example, broadcast signals use full transport streams. These carry not only the content information within the packets, but also the temporal information, which is important for maintaining precise display rates in a television receiver. On the other hand partial transport streams contain only a selected subset of packets, usually filtered based on the packet identifier (PID). From a storage perspective, systems based on partial transport streams are superior to the ones based on full transport. Program streams, used ubiquitously in DVDs, are non-packetized streams of data usually containing only a single compressed program. Systems based on program streams require additional control information to be stored, since the stored content has only limited temporal information
Since content in a transport-stream based PVR/DVR system could originate from a storage medium (and not a broadcast signal), an important problem is reconstructing the stream precisely. All temporal information must be recreated. For full transport streams, a hardware module can read data from the storage medium at a fixed, known rate and recreate the temporal information. However, the problem is more challenging for partial transport streams. Proper gaps for packets that were dropped due to PID filtering have to be recreated. The transport stream reconstruction problem also arises when a partial transport stream has to be recorded on an ISO-61883 compliant storage medium connected via IEEE 1394 interface. For example, the input to a D-VHS tape must be a partial transport stream with very low jitter so that the content can be played back to the digital TV system as precisely as a broadcast signal.